And what do Providers do with all of those envelopes?
I saw a provider recently that, when I set the donation on her night stand, exclaimed in surprise "you put the money in an envelope?" Yes. Doesn't everyone? - I replied. So my question to the board is - do you typically put your "donation" in an envelope? I always do. I am just following the etiquette rules that I read way back when.
Yes, I've always heard money in an unsealed envelope. I suppose this is for plausible deniability
and often along with a "Thank You" card. Just a little gesture of appreciation I enjoy making. Plus, she can reuse the card.
Many, many guys use no envelope, and probably think I'm a mangina for doing what I do. I shed endless tears at the thought! 
Just make sure the donation is correct, follow her rules and be yourself
TY card is a nice touch, You are a classy guy. Got a chuckle about the "mangina" remark. If it makes you feel any better, I don't think you are one.
I do as well. It just seems professional and business like and that's likely the type of woman I'm visiting and enjoying some time with.
I also use an envelope, but strive to hide it on the walk up to the address. Etiquette says the "envelope" can be loosely interpreted. With that idea: I once brought a pair of thigh highs and thought it would be cool to put the donation in the thigh high package. She pulled the hose out and pitched the package, not realizing the donation was in there. Now I stick to the envelope.
I always do and never talk about it, place out on dresser unsealed
And what do Providers do with all of those envelopes?
I always ask that the donation be put in a envelope.....xoxo